Relatively hard materials are often processed for mining and construction. The variety of materials include rock, concrete, asphalt, coal and a variety of other types of earth formations. A number of different methods for reducing the size of these hard materials have been developed. One traditional material size reduction method has been to drill relatively small holes in the material which are then packed with an explosive that is ignited resulting in a rapid and cost effective method of size reduction. However, there are a variety of disadvantages to this technique including the inherent risk of injuries, the production of undesirable noise, vibrations, and dust, and the fact that this process is difficult to utilize in situations where space is limited or where there is a potential risk of causing other gases to ignite.
Due to the above-described disadvantages associated with blasting techniques, alternative methods have been developed for reducing relatively hard materials. The main alternative has been the use of reducing machines having rotary reducing components that move rigid and specialized reducing elements through paths of travel. The reducing components can include rotating drums that move the reducing elements through circular paths of travel. Such drums are typically attached to their corresponding machines so that the positions and orientations of the drum can be controlled to bring the reducing elements into contact with the material being reduced. Alternative reducing components can include boom-mounted chains that carry reducing elements. The chains are typically driven/rotated about their corresponding booms. The reducing elements are mounted to and move along the paths of travel defined by the chains. In use, the booms are moved (e. g., through a pivoting motion) to positions where the reducing elements are brought into contact with the material being reduced.
An example machine of the type described above is disclosed at U.S. Pat. No. 7,290,360. The disclosed machine is a surface excavation machine used for applications such as surface mining, demolishing roads, terrain leveling, and prepping sites for new construction or reconstruction by removing one or more layers of material. Surface excavation machines of this type provide an economical alternative to blasting and hammering and provide the advantage of generating a consistent output material after a single pass. This can reduce the need for primary crushers, large loaders, large haul trucks and the associated permits to transport materials to crushers.
The reducing elements of reducing machines have been developed to withstand the impact loads and abrasion associated with material reduction activities. Reducing elements can be constructed in a variety of shapes and sizes and have been labeled with various terms including cutters, chisels, picks, teeth etc. Typical reducing elements include leading impact points or edges and bases. The bases are constructed to fit into mounting structures that are integrated with drums or chains used to carry the reducing elements during material reducing applications. The harsh environment associated with material reducing applications virtually guarantees that the reducing elements will wear down over time. Thus the reducing elements are designed to be replaceable, while the mounting structures are not intended to be replaced frequently. For example, when a given reducing element becomes worn, it is removed from its corresponding mounting structure and replaced with a new, unworn reducing element.
Often, the tips or edges of the reducing elements have a harder construction (e.g., a solid carbide construction) than the bases of the reducing elements. When using new reducing elements to reduce material, the leading points or edges are exposed to the majority of the impacts and abrasion action. However, once the leading tips or edges becomes worn, the bases are exposed to more impacts and abrasive action. A variety of potential problems can arise when this occurs, including that the bases is less efficient at breaking the material causing inefficient operation. This inefficiency can result in generation of sparks and/or excessive heat which can lead to a risk of explosions, as may occur in a coal mining application where methane gas can be present. Additionally, the bases will typically wear relatively quickly as compared to the leading points or tips. This is significant because the bases prevent the reducing element mounting structures from being exposed to wear. Thus, once the leading edges or points of the reducing elements are worn away, the machines can only be operated for a relatively short period of time before the bases wear away resulting in a situation where the mounting structures of the drums or chains are contacting the material being reduced. Once a reducing elements are worn to this point, there is a risk of causing damage to the mounting structures of the drums or chains. The mountings structures are not intended to be repaired easily, so the resulting potential damage can be difficult and costly to repair.
As a result of these issues, there are significant benefits to replacing reducing elements before the wear has progressed to an unacceptable point. Systems have been designed to monitor the condition of cutters to allow operators to interrupt operation and replace cutters at appropriate times. Example systems for monitoring reducing element wear are disclosed in AT3826832; DE 10015005; and US 2010/0076697. While wear sensing systems exist, improvements are needed in this area.